DE3111517A1 - Process for producing wood pulp - Google Patents

Abstract

A uniform stream of a suspension of mechanical pulp is fed, together with coarse wood residues and splinters contained therein, continuously from a grinder (1) to a cone mill (2) which has two treatment zones with a stationary part and a rotating part, in order to convert all the wood materials present in the suspension into individual fibres. At the same time, the degree of grinding of the wood pulp obtained is measured and adjusted to a desired value by controlling both the power consumption of the cone mill (2) and the degree of grinding thereof. The process can be applied to mechanical wood pulp suspensions which have been produced in normal-pressure or superpressure grinders. The wood pulp obtained has a low splinter content and superior strength properties. The power consumption is less than in known processes.

Description

PATENTANWÄLTE Γ '.. ■ "." ·

dr. V. SCHMiED-KOWARZIK ■ dk. P. WEINMOLD · Munich DIPL.-ING. G. DANNENBERC · dr. D. CUDEL- dipping. S. SCHUBERT- frankiuht

8IECFRIEDSTRA3SE β SOOO MUNICH «O

TEI-EFONi (Q891 835024 + S35025 T (SLEX: 5215679

Case: MoDo 1413

MO OCH DOMSJÖ AKTIEBOLAG
ürnsköldsvik, Sweden

Process for the production of wood pulp

130061/066 «

description

The invention relates to a method for producing ground wood and in particular to a method for reducing it Coarse wood residues, blocks, splinters and shavings during production. During the procedure will be simultaneous the degree of grinding of the wood pulp is set to the desired value.

In the production of wood pulp, they are used as the starting materials used wooden blocks and blocks pressed against a rotating grindstone, whereby the wood fibers loosened up and separated from each other. Wood chips can also be used as the starting material. Of the Grinder can be operated either at atmospheric pressure or overpressure.

130061/0668

During the grinding process, the grindstone is splashed with water, doing it and its surface to cool to clean up. The fibers released from the blocks are placed together with the water in a trough at the lower end of the Collected by the grinder. A problem with this method of grinding is that in many cases it is impossible to completely grind all the blocks or blocks. Therefore, wood residues usually remain back, which in some cases can reach a considerable size, up to 1 m in length and a few cm in thickness to have. In the worst case, the width of the wood residues can reach up to 10 cm. The concentration of the obtained Cut suspension on dry solids is usually 0.4 to 2%.

The coarse wood residues collect in conventional sanders at the bottom of the grinding trough and must be removed manually. Related to grinders that are under work overpressure, however, a process has been developed that enables the wood residues to be separated off automatically. The wood residues and the grinding suspension are then fed to a so-called splinter grinder to shred the wood residues into so-called chips, which are often the size of regular matches. In order to convert the chips into fiber form, it is first necessary to To work up the chips, sieve the cut suspension. After sieving, the chips and the largest part of the ground (so-called rejects) are passed through a disc refiner out, in which they are shredded into individual fibers.

Wood residues removed manually from conventional sanders are usually also processed by a shredder guided. About such wood residues and chips that are contained in the grinding suspension emerging from the grinding trough are to be separated, the cut suspension must through

130061/0668

a vibrating sieve are guided, whereupon the resulting rejects are also fed to the shredder. In connection The grinding is sifted again at the shredder and this is similar to grinding under overpressure Rejected material is fed to a disc refiner for defibration.

From the above it can be seen that the recovery of wood residues from the manufacture of wood pulp is relative is complicated. Another disadvantage of the wood grinding process is that the properties and thus the Working conditions of the whetstones vary. A grindstone that has been used for a relatively long time yields relatively high energy consumption a wood pulp with a low freeness. A grindstone that has been used for a long time must therefore be sharpened again. This is done with a special tool, a degree turning tool, which gives the stone a rough, gives a grooved surface. However, a freshly sharpened stone often gives the wood pulp a higher degree of grinding, than is desirable, while the mechanical strength of the wood pulp is relatively low. In known procedures is it is therefore difficult to obtain a pulp of uniform quality.

The aim of the invention is to overcome these difficulties and to provide a method of making pulp which is a product of uniform quality supplies and in which the degree of grinding of the wood pulp and the energy consumption can be regulated. As in known Method does not ensure that all the blocks fed to the grinder are completely ground, and therefore serious problems are caused by coarse chunks or wood debris that is continuously in the grinding suspension occur and so far in a complicated shredder-sieve-refiner process had to be prepared manually, a further object of the invention is to provide a To create a simpler process for producing a pulp of uniform quality.

130061/0668

According to the invention, coarse wood, wood residues and shavings, which were obtained in a grinder, with simultaneous regulation of the freeness of the wood pulp production wood pulp obtained from wooden sticks or blocks in a process which is characterized in that is that you get the pulp suspension obtained in the grinder and the coarse material and chips contained therein continuously feeds a cone mill known per se, so that all wood materials present in the suspension are successively converted into individual fibers, and the degree of freeness (freeness value) of the defibrated reed suspension with a freeness measuring device measures and automatically regulates to a predetermined target value, wherein the freeness measuring device is equipped with a converter that measures the power consumption of the grinder and the power consumption of the cone mill and also regulates the extent to which the suspension is finely ground in the cone mill.

A cone mill is understood to mean a device that has two treatment zones, an initial comminution zone, in which coarse wood residues and splinters are broken up one after the other into fiber products of the same size (pre-defibrated) and a grinding zone in which the fiber products coming from the grinding zone are of the same Size to be ground into single fibers (finally defibrated). The cone mill is also characterized in that it a stator and a rotor, which at their peripheral areas (the grinding zone) in planar, annular grinding disks pass, between which a tapered, adjustable gap is formed. The rotor part of the device has in the crushing zone the shape of a concave cone which has spirally shaped rods on the surface, which are similar Correspond to bars on the stator surface. Such cone mills are from HYDROLIN AB, Sweden, under the name MOULATOR and from the company CELLWOOD

13QD61 / G668

MACHINERY AB, Sweden, under the name KRIMA M REFINER sold.

As mentioned, this type of cone mill has two treatment zones and further streamlined inlet passages which, together with the spirally extending rods on the rotor, facilitate the feeding of the wood material and promote. The material and especially the coarse wood residues are in the input shredding zone crushed, pre-defibrated and softened when under screw action by gradually tapering Gap between stator and rotor are pressed. In the other zone, the grinding zone, the material is finally defibrated and ground between the peripheral parts of the stator and rotor of the device, these parts being in the form of grinding disks to have. The treated material leaves the grinding zone at its periphery. Because of the special conical design of the inlet part of the device and its crushing zone it has been found possible to use the cone mill To supply wood residues of considerable size. To further facilitate the supply of suspension to the device, can be the last part of the line through which the ground glass suspension is brought up by the grinder and fed into the device, provided with a spiral inside rotating along the inner walls of the pipeline.

When using this type of cone mill it has been found possible proved to be an effective reduction in the splinter content of the wood pulp as it passed through the peripheral parts the grinding zone, which have the shape of grinding disks, to achieve, as the device is particularly in this area is provided with the same type of grinding segments as conventional disc refiners. According to the invention, a

130061/0668

Reduction of the splinters and chips content of the wood pulp during its passage through the cone mill of at least 20% can be achieved.

In addition to the shredding of the splinters and chips, it is also possible to process the fibers obtained mechanically, i.e. to reduce and regulate the degree of grinding of the wood pulp by treating in the cone mill. In this regard it has proven to be suitable to measure the freeness value of the cut suspension according to SCAN-C21-65 during the treatment in the cone mill by a minimum of 10 ml and a maximum of 500 ml.

When carrying out the method according to the invention, it is in particular in pressure grinding, a constant level of the grinding suspension in the outlet zone of the grinder is preferred keep upright. This is done according to the invention with the help of a so-called DP cell (differential pressure cell), the automatically a valve in the outlet tube of the cone mill controls. In the case of pressure grinding, the grinding suspension is separated from a cyclone for the steam after the valve fed. If the grinding takes place in a normal pressure grinder, then the wood pulp from the cone mill can be used directly Screening department, a bleaching department or a paper machine. According to the invention becomes part of the an automatic grinding suspension leaving the cyclone Freeness measuring device supplied, preferably after setting the consistency of the ground glass suspension to a constant value with the help of a consistency regulator,

which in turn regulates the supply of dilution water into the system. It has proven to be important that the consistency of the material supplied to the Freeness ~ measuring device Partial flow is constant. Following the measurement of the freeness value of the partial flow, it is returned to the

130061/0668

Main stream returned. In a particularly preferred embodiment, the automatic freeness measuring device is equipped with a recording device for continuous recording of the freeness of the cut suspension. It is also equipped with a converter that sends control signals to power consumption regulators (electrical Power) both in the grinder and in the cone mill. In this way it is possible to reduce the freeness of the To regulate the grinding suspension and to keep it at a constant value, which is recorded simultaneously with a recorder can be. According to the invention, the power consumption of the cone mill never exceeds 800 kWh / t of produced wood pulp. By setting a certain setpoint for the freeness of the wood pulp, it is therefore possible to use the automatic freeness measuring device to continuously produce wood pulp with the desired freeness value. The wood pulp leaving the cyclone can be fed in a suitable manner to a dewatering device in order to Recover hot process water, which can be used with advantage as splash water in the grinder. Possibly the thickened wood pulp can then be bleached and finally sieved. Alternatively, you can use the After thickening, first thin, sieve and then bleach the wood pulp.

In order to influence the roughness of paper, the thickened wood pulp can alternatively be fed to a conventional disc refiner for the final setting of the grinding degree. This type of treatment is called "post refining" known. In this treatment of the wood pulp, bleaching chemicals can also advantageously be added to the material flow what is referred to as "refiner bleaching".

When pressure sanding, i.e. when using an under pressure working grinder, the reed suspension leaving the cone mill is preferably sent directly to a pressure

130061/0668

sieve fed for sorting. If the pressure of the grinder exceeds 100 kPa (1 kp / cm ^a ), no pump is required. In this case, the setting of the consistency of the material is also preferably done upstream of the cyclone, ie in the line between the pressurizer and the cyclone. However, the pressure screen can also be arranged behind the cyclone without any disadvantage.

In the method according to the invention, in which the grinding suspension leaving a grinder in a continuous and a steady stream is fed to a cone mill, it is possible to remove all of the heavy parts present in the suspension or to convert wood residues regardless of their size into Paser form and at the same time a wood pulp Get consistent quality by checking the power consumption of the grinder and the cone mill as well regulates the circumferential gap of the mill, surprisingly has it has also proven possible to break up long and relatively coarse wood residues without disrupting production and grind.

According to the invention it is also possible to adjust the freeness of the wood pulp with relatively moderate power consumption to reduce and adjust what a surprising and important Represents advantage.

There is another advantage achieved according to the invention in that it is possible to use a freshly sharpened whetstone with a low freeness wood pulp to manufacture. The surprisingly high strength properties of the wood pulp produced according to the invention are also a significant advantage.

130061/066 *

There are also important advantages on the energy side, as it is possible, for example, to remove steam from the cyclone during pressure grinding to be used for heating purposes or to generate electrical energy. Also worth mentioning is the comparison to known ones Process reduced total energy consumption by the manufacturer 1 management procedure see chap.

In the following the invention is illustrated by means of preferred embodiments explained in more detail with reference to the flow diagram shown in the drawing.

Comparative example 1

A grinding suspension from a conventional normal pressure grinder with a freshly sharpened grindstone is fed to a vibrating sieve to separate coarse material and chips. The usable wood pulp leaving the sieve is collected in a container. The reject, i.e. gross Wood residues and chips »are fed to a shredder, in which they are cut to a maximum length of about 40 mm be crushed. The scrap treated in the grinder is then mixed with wood pulp from the vibrating screen. Samples are taken from the mixture obtained for analysis and paper listening. Before making The substance mixture is sieved from sheets of paper through a flat laboratory sieve, the sieve plate of which is 0.15 mm wide Has. A test sheet is then made from the wood pulp. The analysis and the test results are given in Table I.

Comparative example 2

A joint suspension from a pressure of 100 kPa (approx. 1 kp / cri) working grinder equipped with a freshly sharpened whetstone, is fed to a shredder,

130061/0668

- yt -

around coarse wood residues contained in the suspension and To shred chips. The cut suspension is then from fed to the shredder in a cyclone in order to separate steam from the suspension. Following the cyclone is a Sample of the wood pulp taken for analysis and for the production of a test sheet similar to Comparative Example 1. The results are given in Table I.

Example 1
(According to the flow diagram shown in the drawing)

A ship suspension from that used in Comparative Example 2 used pressure grinder 1 (overpressure 100 kPa) is one Cone mill 2 supplied, in the coarse wood residues, Splinters and shavings are transferred to Paserforra. the Ship suspension in the outlet zone of the grinder is with Using a "DP cell" 3 continuously on essentially held the same level in-which the cell 3 the outlet opening a valve 4 regulates, which is directly connected to the cone mill is provided in the derivative 5 of the cone mill. Make the passage of valve 4 the cut * suspension fed via line 5 to a cyclone 7 in order to separate steam 6 from the suspension. In the shown Embodiment is the discharge 8 of the cyclone with a sensor 9 for determining the consistency of the material and an associated one Measuring and control unit 10 is provided, which in turn controls a valve 11 in the dilution water line 12. In this way the ship's suspension is reduced to what is necessary Diluted to a degree to maintain a constant consistency of the fabric. In Comparative Examples 1 and 2, the consistency of the ship's suspension after leaving it is of the grinder more than 2%, in the present case, however, a constant material consistency of 2% can be achieved with the help of the named automatic measuring and control unit 10 upright-

can be obtained.

130061/066 $

Part of the flow of the pulp suspension, its consistency has been set, is then fed to an automatic freeness measuring device 13, which reads the freeness values the ship suspension with a recorder 14 records. In this example, the cone mill 2 is operated with the largest possible grinding gap. Here is the power consumption 60 kW. The production is at the same time 2.3 t / h, so that the specific power consumption achieved in this experiment 26 kWh / t bone-dry wood pulp.

The recorder 14 of the freeness measuring device shows a freeness value of about 220 ml. With simultaneous determination the freeness with a Canadian standard freeness measuring device a value of 200 ml is obtained. The agreement between the two values is therefore very good. As in the comparative examples 1 and 2 described, wu. len swatches taken to determine the fabric and paper properties. The results are given in Table I.

Example 2

Another experiment is carried out according to Example 1 using the grinding suspension from the grinder described there carried out, but the power consumption of the cone mill is increased from 60 kW to 200 kW. Surprisingly causes this change in performance does not change production capacity; i.e. the production remains unchanged at 2.3 t / h. However, the specific power consumption increases in this case to 87 kWh / t.

By reducing the grinding gap and increasing the output the cone mill reduces the freeness value to 145 ml. As in the previous example, a sample is taken and examined. The results are given in Table I.

130061/066 «

Example 3

Another experiment is carried out according to Examples 1 and 2 using the grinding suspension from the grinder carried out by Example 1, but increasing the Power consumption of the cone mill to 300 kW. Surprisingly, this has no effect on the production capacity, although the grinding gap was further reduced. The specific power consumption is calculated at 130 kWh / t. A swatch is used for analysis and to determine its properties as in the previous examples taken. The results are given in Table I.

13ÜÖ61 / 0668

Table I.

State of the art

invention

Comparative example example

Power consumption in the grinder, kWh / t

Power consumption in the shredder, kWh / t

Power consumption in the cone mill, kWh / t

Freeness, CSF, ml

Chip content (Sommerville) 4.0 % (0.15mm)

Fiber fractionation

Bauer-McNett, + 20 mesh,%

+150 mesh,%

-150 mesh,%

Tensile index, Nm / g tear index, mNra ³ / g bulk density, kg / öi ^s

750

15th

250
3.9

1
75Ο

26th

220
2.8

2 75Ο

87 13Ο

145 105 1.9 0.7

11 21st 22nd 24 24 62 54 53 52 52 27 25th 25th 24 24 21st 28 33 36 41 3.1 4.8 5.1 5.3 5.6 315 310 335 345 355

From Table I it can be seen that in the invention A surprisingly high decrease in the splinter content is achieved if the grinding suspension in a method Cone mill treated. Far more surprising, however, is that The fact that it has been shown to be possible to have coarse wood residues and long chips in this mill without production disruptions to treat. Another surprising and unexpected fact is the ability to adjust the grind to reduce the grinding suspension by a relatively small increase in energy consumption.

130061/0668

- V6 "~

Another important advantage of the method according to the invention is that a wood pulp with low Freeness value can be established even if the whetstone has been re-sharpened. As can be seen from Table I. is, the strengths of the wood pulp produced according to the invention are compared to that according to known Method obtained substance surprisingly good.

For further. Comparison between the method of the invention and known methods, the experiments described above are repeated, but a grindstone is used, which was in continuous operation for 8 days.

Comparative example 3

The procedure of Comparative Example 2 is repeated, however Instead of a newly sharpened whetstone, you use a whetstone that has been in use for 8 days. The results are given in Table II.

Example 4

The procedure of Examples 1 to 3 is repeated, however you use a whetstone that has already been in use for 8 days. The power consumption of the cone mill is reduced to one Average value set, namely about 160 kW. The results are given in Table II.

130061/066 *

Power consumption in the grinder, kWh / t in the shredder, kWh / t in the cone mill, kWh / t Freeness, (CSF), ml

Chip content (Sommerville) (0.15 mm),%

Bauer-McNett fiber fractionation:

Table II Example 4 Comparison
example 3 950 1100 - 15th 70 - 140 150 1.2 ^le) 3.3

+ 20 mesh,% 20th 23 + 150 mesh,% 50 52 - 15O mesh,% . 30th 25th Tensile index, Nm / g 37 36 Tear Index, mNm ^a / g 5.4 5.6 Bulk density, kg / m ³ 350 345

From Table II it can be seen that the total power consumption in the process according to the invention surprisingly about 100 kWh / t lower than in the known process. Furthermore, a wood pulp is used in the method according to the invention obtained with a far lower splinter content than in the known process. According to the invention, the splinter content is reduced by practically 65% if wood pulp is used with a blunt grindstone while maintaining lower power consumption becomes, which is an important benefit.

130061/0668

The values given in the tables are determined according to the following SCAN standards (Scandinavian Pulp, Paper and Board Testing Committee):

Freene s s: SCAN-C 21:65

Splinter grade: Sommerville

Fiber fractionation: SCAN-M 6:69

Tensile and tear index as well as bulk weight: SCAN-C 28:69.

130061/0668

-ao-

Blank page

Claims (5)

Patent claims Process for the production of wood pulp from wood and blocks, characterized in that a grinding suspension is obtained from a grinding machine together with the coarse matter and splinters contained therein continuously a cone mill known per se so that all wood materials present in the suspension are successively converted into individual fibers, and the freeness (preness value) of the defibrated grinding suspension obtained with a preness measuring device automatically measures and regulates to a predetermined target value, wherein the Freeness measuring device has a converter that the Power consumption of the grinding machine, which regulates the power consumption of the cone mill and its degree of grinding, 2. The method according to claim 1, characterized in that the content of coarse materials and fragments in the from Grinding machine cut obtained when passing through the cone mill is reduced by at least 20%. 130061/0668 3. The method according to claim 1 or 2, characterized in that the freeness value of the ship suspension during the treatment in the cone mill by at least 10 ml and Is reduced to a maximum of 500 ml. 4. The method according to claims 1 to 3, characterized in that the power consumption when treating the
Ground suspension in the cone mill has a maximum of 800 kWh / t grinding achieved. 5. The method according to any one of claims 1 to 4, characterized in that the control pulses of the converter
Freeness measuring device can be set according to a freeress setpoint value which is predetermined for each individual case, or set to freeness setpoint values which are preselected during production. 130061/0668